Drive unit for motor vehicle

ABSTRACT

Drive unit for motor vehicles, comprising an internal combustion engine ( 2 ), an accelerator pedal and an electronic engine control unit ( 15 ) arranged for controlling engine torque and r.p.m. The accelerator pedal is electrically connected to the engine control unit. During acceleration, the engine control unit controls the torque as a function of engine speed for various accelerator pedal positions, as determined by a first computer matrix stored in the control unit, which provides a predetermined additional torque when there is a certain reduction in engine speed. After constant or practically constant vehicle velocity has been achieved at a constant accelerator pedal position, the engine control unit controls the torque as a function of engine speed along a second stored computer matrix, which provides a predetermined greater additional torque when there is said predetermined reduction of the engine speed.

The present invention relates to a drive unit for a motor vehicle,comprising an internal combustion engine, a manually adjustable throttlecontrol and an electronic engine control unit for controlling the enginetorque and engine speed, and to which the throttle control iselectrically connected, a first computer matrix plotting engine torqueas a function of engine speed for various throttle control positionsbeing stored in said engine control unit and having in a diagram a firstslope for the curves for the throttle control positions.

It has become more and more common in motor vehicles of late to replacea mechanical wire linkage system coupling the accelerator pedal positionor its movement to the engine throttle and fuel engine system withelectronic transmission for controlling engine torque and speed. Asensor coupled to the accelerator pedal provides signals representingthrottle control position to an electronic control unit, commonly in theform of a microprocessor, which controls engine functions as a functionof the sensed throttle control position. To achieve this, a computermatrix mapping engine torque as a function of r.p.m. for variousthrottle control positions is stored in the control unit.

The matrix should preferably be constructed so that the control unitprovides even acceleration for each throttle control position, i.e. withas little jerking as possible when shifting during the acceleration.This is achieved with relatively flat throttle control curves. At thesame time the control unit, after having reached the target velocity atconstant throttle control position, should be able to maintain thisvelocity with very small deviations. This, however, is achieved withthrottle control position curves which are as deep as possible. Steepcurves provide large increases in torque for a minor drop in r.p.m. andspeed. When this occurs, however, when shifting up with accompanyingreduction in r.p.m., this provides more additional torque than what isdesirable and can lead to uneven driving. For these reasons, up to now athrottle control position matrix has been stored in the control unit,which is as good a compromise as possible between control during theacceleration of the vehicle and during cruise operation.

The purpose of the present invention is to achieve a drive unit of thetype described by way of introduction, which has a control unit whichcan control the engine so that the vehicle will be provided with atleast almost constant acceleration and a constant velocity when thethrottle control position is held constant.

This is achieved according to the invention by virtue of the fact that asecond computer matrix, plotting engine torque as a function of enginespeed for various throttle control positions, is stored in the enginecontrol unit, that the curves for the throttle control positions in thediagram of the second matrix have a steeper slope than the curves in thediagram of the first matrix, and in that the engine control unit isdisposed, at a setting of the throttle control giving rise to anacceleration exceeding a predetermined minimum acceleration, to controlthe engine torque and engine speed along the curves in the first matrixdiagram and, upon a signal indicating a drop below said minimumacceleration, to control the engine torque and engine speed along thecurves in the second matrix diagram, so that for a certain change inengine speed, a greater change in torque will be provided than whencontrolling along the curves in the first matrix diagram.

By the design according to the invention, the first matrix can beoptimized for comfortable, smooth acceleration when shifting at constantaccelerator pedal position, and the second matrix can be optimized forconstant velocity at constant accelerator pedal position. When constantvelocity has been achieved after acceleration, i.e. when theacceleration has returned to zero or almost zero, the control unitshifts from control along the throttle control curves of the firstmatrix to control along the curves of the second matrix, which meansthat even a small reduction in r.p.m./velocity due to an increase indriving resistance, e.g. a hill, will result in a greater increase intorque and more rapid correction of the velocity than if the firstmatrix would be the governing matrix, which would only have provided thecorre-sponding additional torque after a much greater reduction in ther.p.m./velocity. If the driver opens the throttle to accelerate, thecontrol unit will switch back to the first matrix.

In a preferred embodiment of the drive unit according to the invention,comprising a stepped gearbox coupled to the engine, the slopes of thecurves in the first matrix are selected so that they approximate theincrements in the gearbox. This means that, at constant throttle controlposition, the output torque from the gearbox, prior to and aftershifting between adjacent shift positions, will be at leastapproximately constant. By virtue of the fact that the output torque isthe same prior to and after shifting, the unavoidable little break intorque delivery, when the clutch between the engine and the gearbox isreleased, will be unnoticed and the acceleration will be experienced asbeing constant.

The invention will be described in more detail below with reference toexamples shown in the accompanying drawings, where

FIG. 1 shows a schematic representation of an internal combustion enginewith connected clutch and gearbox,

FIG. 2 is a diagram of a previously known throttle control positionmatrix,

FIG. 3 is a diagram of a first throttle control position matrixaccording to the invention, and

FIG. 4 is a diagram of the throttle control position matrix in FIG. 3,together with a second throttle control position matrix.

The drive unit 1 shown in FIG. 1 comprises in the embodiment shown asix-cylinder engine 2, e.g. a diesel engine, the crankshaft 3 of whichis coupled to an automated drive disc clutch generally designated 4,which is enclosed in a clutch housing 5. The crankshaft 3 isnon-rotatably joined to the clutch housing 6 of the clutch 4, while itsdisc 7 is non-rotatably joined to an input shaft 8, which is rotatablymounted in the housing 9 of an autoshift gearbox generally designated10, which in the example has a splitter group 11, a main group 12 and arange group 13. The gearbox 10 has an output shaft 14 intended to bedrivably coupled to the vehicle driving wheels, e.g. via a propellershaft.

The engine 2 is controlled by an electronic engine control unit 15,which can comprise a microprocessor, in response to signals from aposition sensor 17 coupled to a throttle control 16, e.g. an acceleratorpedal. The transmission 10 is controlled by a transmission control unit18, which can comprise a microprocessor in response, firstly, to theposition of a manual gear selector 19 and, secondly, to controlparameters including accelerator pedal position and engine r.p.m. fedinto the control unit 18. The transmission control unit 18 communicateswith the engine control unit 15 as well. The gear selector 19 has aneutral position N and two automatic drive positions D (forward) and R(reverse) and possibly other positions, permitting the driver to shiftmanually. In positions R and D, the transmission control unit 18 shiftsautomatically when starting and driving.

The diagram in FIG. 2 illustrates how previously known engine controlunits have usually been programmed for controlling engine torque as afunction of engine speed for various throttle control positions. Drawninto the diagram are throttle control positions curves A representingfrom 10% up to 90% of full throttle opening. B indicates the full loadlimit of the engine. As can be seen from the diagram, no extra torque isobtained between circa 80% and 100% of full throttle opening, sincethese curves lie outside the full load limit. At point C on curve Arepresenting 50% throttle opening, the engine speed is 1600 r.p.m. andthe torque circa 200 Nm. If the transmission ratio in this gear is1.25:1, a torque of circa 250 Nm will be provided at the output shaft ofthe gearbox. After shifting up to a gear with ratio 1:1 at constantthrottle opening, i.e. still 50%, the r.p.m. will drop to 1280 r.p.m.and the torque will increase to 850 Nm, as can be seen at point D. Thetorque at the output shaft of the gearbox and thus also to the drivingwheels will thus increase more than three times. With the slopes of thethrottle control position curves as shown, a reduction in r.p.m. fromcirca 1600 r.p.m. to circa 1500 r.p.m. (prior to shifting) will increasethe torque only to 400 Nm, which means that, if the resistance increaseswhen driving up a hill, for example, the velocity will drop markedlybefore the additional torque is sufficient to counter the drop invelocity.

FIG. 3 shows a diagram of a computer matrix according to the inventionfor controlling the torque as a function of engine speed for variousthrottle control positions during acceleration. The diagram showsthrottle control position curves representing 20% up to 100% of fullthrottle opening. The curve B indicates as above the full load limit ofthe engine. At point C on the curve A representing 40% of full throttleopening, the engine speed is 1600 r.p.m. and the torque is 820 Nm. Witha ratio as above of 1.25:1 in the gear speed in question, the torque atthe output shaft of the gearbox will be 1025 Nm. After shifting up to agear speed with the ratio 1:1 with constant throttle opening, i.e. still40%, the engine speed will drop to 1280 r.p.m. at the same time as thetorque at the output shaft of the gearbox will rise to 1025 Nm, i.e. thesame torque as prior to shifting.

FIG. 4 shows the diagram of FIG. 3 with a throttle control positioncurve G for controlling the torque as a function of engine speed whendriving at constant velocity. During acceleration with 40% throttleopening, the torque and the engine speed are controlled along the curveA. At C it is assumed that constant or nearly constant vehicle velocityhas been achieved. Thereafter, the transmission control unit 18 switchesover the engine control unit 15 to control the torque as a function ofengine speed along the curve G, which is preferably as steep as possiblefor better maintenance of constant velocity. The curve G cannot,however, be infinitely steep. Essen-tially, the curve G can be said tobe described by y=k×x+m, where y=torque, k=slope, x=r.p.m. determineswhere along the 40% curve G is to be placed, i.e. where the accelerationis about zero. m is target velocity controlled (selected constantvelocity). The negative slope of G (i.e. k) is primarily dependent onengine speed. In certain cases it can be desirable to have a less steepslope at low r.p.m. than at high r.p.m., i.e. if the acceleration iszero at 800 r.p.m. and 20% throttle opening, the throttle controlposition curve through this point will not have as steep a slope as thatintersecting that of point C. The less steep slope is selected here toreduce the risk that the drive chain will self-oscillate at lower r.p.m.Less steep slope at low r.p.m. will make the system smoother and lesssensitive. Self-oscillation can be triggered, for example by drivingover a bump. Self-oscillation tendencies in the drive chain have to dowith the elasticity of the drive chain, its stiffness, anchoring andwhat gear ratio is engaged at the time in question. A flattening of thethrottle control position curve G at low torque (under 200 Nm) similarto the curves in FIG. 2 is also conceivable. If the driving resistanceincreases at the same time as the driver maintains constant throttleopening, there will be a substantially greater additional torque for agiven drop in speed, which is revealed by the diagram in FIG. 4. With adriving resistance resulting in a drop in engine speed from 1600 r.p.m.to 1500 r.p.m., the torque will increase from 820 Nm to circa 1250 Nmwith control along the curve G. For the engine to provide the sametorque when controlling along the curve A, the r.p.m. would have to dropto less than 1100 r.p.m.

As soon as the driver changes the throttle control position, the enginecontrol unit will switch to controlling the torque along the curves A.The control unit 15 is, how-ever, preferably programmed to disregardminor accelerator pedal movements which can be caused by bumps in theroad. For shifting torque control in accordance with one or the othermodel, the acceleration does not need to be absolutely zero forswitching to control along the curve G. Rather, the control unit can bedisposed to switch when the acceleration drops below a pre-programmedminimum value.

The invention has been described above with reference to throttleopening control with an accelerator pedal, but of course also applies tohand-operated controls, i.e. those used to raise or lower the cruisecontrol speed.

1. Drive unit for a motor vehicle, comprising an internal combustionengine (2), a manually adjustable throttle control (16) and anelectronic engine control unit (19) for controlling the engine torqueand engine speed, and to which the throttle control is electricallyconnected, a first computer matrix plotting engine torque as a functionof engine speed for various throttle control positions being stored insaid engine control unit and having in a diagram a first slope for thecurves (A) for the throttle control positions, characterized in that asecond computer matrix plotting engine torque as a function of enginespeed for various throttle control positions is stored in the enginecontrol unit (15), that the curves (G) for the throttle controlpositions in the diagram of the second matrix have a steeper slope thanthe curves (A) in the diagram of the first matrix, and in that theengine control unit is disposed, at a setting of the throttle control(16) giving rise to an acceleration exceeding a predetermined minimumacceleration, to control the engine torque and engine speed along thecurves (A) in the first matrix diagram and, upon a signal indicating adrop below said minimum acceleration, to control the engine torque andengine speed along the curves in the second matrix diagram (G), so thatfor a certain change in engine speed, a greater change in torque will beprovided than when controlling along the curves in the first matrixdiagram.
 2. Drive unit according to claim 1, comprising a steppedgearbox (10) coupled to the engine, characterized in that the slope ofthe curves (A) in the first matrix diagram are selected so that theslope approximately corresponds to the gearshift increments in thegearbox, whereby, at constant throttle control position, the outputtorque from the gearbox prior to and after shifting between adjacentgear positions will be approximately constant.
 3. Drive unit accordingto claim 2, characterized in that the stepped gearbox (10) is anautoshift gearbox, which is controlled by an electronic control unit(18), which, when a gear selector (19) is in an autoshift position,selects the gear speed in response to various parameters includingengine speed and throttle control position, and that the gearbox controlunit determines the selection of matrix in the engine control unit.